This is a phase I, multiple-dose, four-arm, drug-interaction pharmacokinetic study to determine if giving a combination of FDA-approved anti-HIV drugs (protease inhibitors) affects drug levels of FDA-approved lipid-lowing drugs, and vice versa. The three protease inhibitors used in this study are nelfinavir, ritonavir, and saquinavir. The three lipid-lowering drugs are pravastatin, simvastatin, and atorvastatin. The GCRC will be used to dispense medications and to perform phlebotomy.